1. Field of the Invention
The present invention generally relates to an optical pick-up device, and in particular, an optical pick-up device having an optical system for irradiating an optical disk with laser light. The optical pick-up device is structured to control a laser light-emitting device for keeping the emission power of the laser light-emitting device constant by detecting the amount of the light outside an effective diameter of an objective lens of the laser light emitted from the laser light-emitting device.
2. Description of the Related Art
Recent years, apparatuses for CD-ROM, CD-R, CD-RW, etc. using an optical disk as a recording medium have been employed as information recording/reproducing apparatuses for a personal computer, etc. These information recording/reproducing apparatuses contain an optical pick-up device structured so that laser light is irradiated onto the optical disk so as to record information and light reflected from the optical disk is detected so as to read the information.
For the kind of information recording/reproducing apparatus, it is necessary to obtain an output level of the laser light for irradiating the optical disk in order to perform stable recording and reproducing process. Accordingly, the optical pick-up device has a laser-light amount detecting unit for detecting an intensity of laser light emitted from a semi-conductor laser which device is structured so as to control or adjust the intensity of the laser light emitted from the semi-conductor laser according to need, based on the intensity of the laser light detected by the laser-light amount detecting unit.
FIG. 1 is a schematic diagram showing one example of a conventional optical pick-up device with light rays from a laser light-emitting device. The optical pick-up device generally includes a semi-conductor laser 1 (a laser diode), a beam splitter 2, a light amount detecting device 3, a collimator lens 4, a directional control mirror 5, and an objective lens 6. In the optical pick-up device, an optical disk 7 is subjected to such a recording/reproducing process that laser light is irradiated onto the optical disk 7 and reflected light is detected and processed.
The laser light (divergent light) emitted due to oscillation of the semi-conductor laser 1 enters the beam splitter 2 and part of the laser light is separated in the beam splitter 2 and enters the light amount detecting device 3.
Output current from the light amount detecting device 3 is approximately proportional to the amount of the laser light passing through the beam splitter 2 and being irradiated onto the optical disk 7, via the collimator lens 4, the directional control mirror 5, and the objective lens 6. Accordingly, the amount of the laser light irradiated onto the optical disk 7 can be adjusted according to need by monitoring the amount of the laser light that enters the light amount detecting device 3 and controlling driving current of the semi-conductor laser 1. Thus, the laser-light amount detecting unit includes the beam splitter 2 and the light amount detecting device 3.
However, since the laser light emitted from the semi-conductor laser 1 is separated in the beam splitter 2 and introduced onto a photo-detection part 9 of the light amount detecting device 3 in the structure of the optical pick-up device (laser-light amount detecting unit) shown in FIG. 1, the problem is that the amount of light for irradiating the optical disk 7 is reduced by the amount of the separated laser light.
Then, in order to solve the problem of the optical pick-up device shown in FIG. 1, an optical pick-up device shown in FIG. 2 has been proposed. The optical pick-up device shown in the FIG. 2 is structured so that the beam-splitter 2 is not used, so as to avoid the loss of the amount of the light.
Specifically, provided is the structure of setting the light amount detecting device 3 at a position inside an area irradiated with the laser light (divergent light) emitted from the semi-conductor laser 1 and outside the effective diameter of the objective lens. The laser light outside the effective diameter of the objective lens (referred to xe2x80x9cleakage lightxe2x80x9d, below) does not irradiate the optical disk 7. If the leakage light outside the effective diameter of the objective lens enters the light amount detecting device 3, the amount of light for irradiating the optical disk 7 is not reduced.
In addition to the above structure shown in FIG. 2, also provided is such a structure that a reflecting mirror 8 is arranged between the semi-conductor laser 1 and the collimator lens 4 as shown in FIGS. 3(A) and (B), in which part of the laser light is emitted from the semi-conductor laser 1, reflected to a lateral side at which the light amount detecting device is provided, and received on the photo-detection part 9 of the light amount detecting device 3. In the case of the structure shown in FIGS. 3(A) and (B), since the leakage light outside the effective diameter of the objective lens irradiates the photo-detection part 9 of the light amount detecting device via the reflecting mirror 8, the amount of light for irradiating the optical disk 7 is not reduced.
FIG. 4 shows a light intensity distribution of the laser light at the set position of the light amount detecting device 3 in the optical pick-up device shown in FIG. 2 (or the reflecting mirrors 8 shown in FIGS. 3(A) and (B)). In the optical pick-up device shown in FIG. 2, as shown in FIG. 4, provided is such a structure that light amount detection is performed in the irradiated area with the leakage light outside the effective diameter of the objective lens by utilizing beam broadening in the vertical direction of the semi-conductor laser 1 (or a tangential direction on the disk surface).
However, as shown in FIG. 4, when the light irradiates the total area of the photo-detection part 9 of the light amount detecting device 3, the light intensity may be increased suddenly and the amount of light received at the light amount detecting device 3 may become equal to or more than a necessary light amount.
As a method for solving such problem, for example, provided is such a structure that a light amount limiting member for limiting the light amount is provided in front of the light amount detecting unit and part of light passing through a hole (pin-hole) provided on the light amount limiting member irradiates the photo-detection part of the light amount detecting device, as is disclosed in Japanese Laid-Open Patent Application No. 7-105567. Also, a method for adjusting photo-detection sensitivity of the light amount detecting device 3 using an electric circuit as shown in FIG. 5 has been proposed. The electric circuit is configured such that output (sensitivity) to a front monitor is adjusted by varying a feed back resistor of an operational amplifier AMP. That is, I/V conversion of an output from the light amount detecting device 3 is performed by adjusting the resistor value of a variable resistor VR. Herein, a phase compensation condenser C for adjusting a response waveform from the operational amplifier AMP is also optimized.
However, for the structure with use of the light amount limiting member as disclosed in the aforementioned patent application, since the amount of the leakage light that irradiates the light amount detecting device changes dependent on an output property of the semi-conductor laser, etc., it is necessary to prepare a plurality of light amount limiting members with a hole having a individual diameter and to exchange the light amount limiting members in accordance with the amount of light received on (or photo-detection sensitivity of) the light amount detecting device.
Thus, in the conventional optical pick-up device, the problem is that it has to be confirmed that the amount of light received on the light amount detecting device is an optimum value when the light amount limiting members are exchanged in order to adjust the amount of light to be received on the light amount detecting device to an optimum value and accordingly that exchange operation is a bother.
Also, when the photo-detection sensitivity of the light amount detecting device 3 is adjusted employing the electric circuit as described above (see FIG. 5), the optimization of the phase compensation condenser C has to be performed in accordance with adjustment of the feedback resistor by the variable resistor VR, but the problem is that only a coarse adjustment with a tolerance of the condenser C is allowed, since that adjustment operation is complex and an accurate adjustment is difficult.
It is a general object of the present invention to provide an optical pick-up device capable of adjusting an amount of light to be received on a light amount detecting device, in which the above disadvantages are eliminated.
The above object of the present invention is achieved by an optical pick-up device including:
an optical system that irradiates light emitted from a light-emitting device through an objective lens onto a recording medium;
a light amount detecting device that receives and detects light outside an effective diameter of the objective lens in the light emitted from the light-emitting device; and
a light amount adjusting member that adjusts an amount of the light to be received on the light amount detecting device, provided between the light-emitting device and the light amount detecting device.
The above object of the present invention is also achieved by an optical pick-up device including:
an optical system that irradiates light emitted from a light-emitting device through an objective lens onto a recording medium;
a reflecting mirror that reflects light outside an effective diameter of the objective lens in the light emitted from the light-emitting device;
a light amount detecting device that receives and detects light reflected from the reflecting mirror, provided in an optical path of the light from the reflecting mirror; and
a light amount adjusting member that adjusts an amount of the light to be received on the light amount detecting device, provided between the reflecting mirror and the light amount detecting device.
Furthermore, the light amount adjusting member may include a baffle provided rotatably at a position opposing to a receiving surface of the light amount detecting device, wherein the amount of the light to be received on the light amount detecting device is adjusted dependent on a rotational angle of the baffle.
Moreover, the light amount adjusting member may include a baffle provided slidably at a position opposing to a receiving surface of the light amount detecting device, wherein the amount of the light to be received on the light amount detecting device is adjusted dependent on a slide position of the baffle.
According to the invention described above, the amount of light to be received on the light amount detecting device can be adjusted easily, and precision for light amount detection by the light amount detecting device can be improved so as to stabilize the precision for the detection. Also, in the case of employing the electric circuit, since the feedback resistor can be set at a fixed value by providing the light amount adjusting member, optimization of the phase-compensation condenser C can be omitted so as to simplify the adjustment operation. In addition, a conventional laborious operation of exchanging light amount limiting members is not required and the amount of light to be received on the light amount detecting device can be adjusted to an arbitrary value for a short time.